Changes to GCSE grades could mean half as many students are awarded the top mark of A* in a bid to show exceptional performance, the exam watchdog has suggested.

A new marking system of 1-9 will be introduced to secondary schools in England from next year as part of an overhaul of GCSE exams.

Ofqual is considering whether to set the grade 9 boundary, the highest possible, so it is awarded to only 50% of the current number of students achieving an A* to distinguish between the brightest students.

It is one of a number of proposals put forward by the watchdog on how it should set and maintain performance standards.

They include whether the standard for a grade 5, one below the current grade C, should be internationally benchmarked in line with the best performing countries.

Chief regulator Glenys Stacey said: "How standards are set and maintained, in effect where we set the bar and how we hold it steady, are extremely important issues.

"We want to hear from students, parents, employers, higher and further education school leaders and teachers about our proposals.

"It is vital that people engage with these issues, as many will need to think about how they will use the new grading structure to make decisions about students applying for work or education opportunities. And we will be working hard to help them understand the new system as 2017 approaches."

The proposals also ask whether grade 4 or grade 5 should become the expected pass grade, for measures such as school league tables and minimum standards for schools.

The first wave of tougher GCSEs in maths, English language and English literature will be introduced next year, with the new qualifications awarded in August 2017.

Further subjects are due to be introduced for first teaching in 2016, including geography, history, biology, physics and double science.

Ofqual also intends to introduce a new reference test to be taken by a sample group of Year 11 students so examiners can monitor the performance of different year groups.

The test will be piloted in 2016 and run annually from 2017 when the first 1-9 grades are awarded.

Ofqual says it wants to continue to use and improve the current approach of awarding grades.

Ms Stacey added: "The anchor point with the new grade 4 and current grade C will provide some valuable certainty for people as the first new GCSEs are awarded in 2017.

"If the proposals for grades 4 and 5 go ahead, the Government can consider how the new grading scale will be reflected in the accountability regime.

"There is still much to do, but we know that teachers will want as much time as possible to understand the new grading system and familiarise themselves with the new qualifications.

"That is why we aim to have decisions made about setting standards and the new specifications in school this autumn, a year ahead of first teaching."